The present invention relates to an ATM (Asynchronous Transfer Mode) switch that exchanges ATM cells. More particularly, the present invention relates to a large scale ATM switch that can be expanded with hardware in proportion to increase in capacity, wherein the expanded ATM switch does not internally block traffic flow.
Various structures for large scale ATM switches have been proposed. Such large scale ATM switches are intended to increase the speed and permit the implementation of a large scale ATM communications in a communication network. An example of a large scare ATM switch is described in Japanese patent Laid-open Publication 4-98937 corresponding to U.S. Pat. No. 5,557,621. The large scale ATM switch described therein is a cell division type ATM switch. A cell division type ATM switch divides an ATM cell into a plurality of partial cells, and exchanges the partial cells with a plurality of ATM switch units. Each of the ATM switch units are independently operated and can properly be used to increase the capacity of an ATM switch.
However, in the cell division type ATM switch described above, it is necessary to add the same header to all of the partial cells. If there are a large number of partial cells throughput of the ATM switch decreases due to the fact that the portion of each partial cell occupied by the header increases. Further, if the size of a cell is fixed, a limit arises in the number of cell partitions that can be performed. In other words, when a fixed-length cell is used, increases in capacity of an ATM switch is limited when the switch is a cell division type ATM switch.
Another cell division type ATM switch is described in Japanese patent Laid-open Publication 2-67045. This switch slices a cell into a plurality of signals, and exchanges the signals with a plurality of subswitches. In this type of ATM switch, a limit arises in bit-slicing a cell similar to the cell-division type ATM switch disclosed in 4-98937. Thus, a limit also arises in the capacity of the ATM switch disclosed in 2-67045.
FIG. 2 illustrates a known structure of a large scale ATM switch. This switch connects a plurality of ATM switch units, which have predetermined exchange abilities to form an ATM switch matrix. In this switch the blocking of traffic does not occur in spite of the large scale nature of the switch. Further, this switch can be easily expanded to provide even larger capacity. However, a disadvantage of the ATM switch matrix is that desired increases in capacity requires increasingly larger amount of hardware to accomplish the increases. Therefore, this switch is not suitable for use in an exchange system wherein size considerations are important.
Another large scale ATM switch is described in an article xe2x80x9cConfiguration of ATM Switching Networks which are Non-blocking at Call Levelxe2x80x9d by Sesaki et al., The Transaction of the Institute of Electronics, Information and Communication Engineers, B-I, J76-B-B, No. 1, pp. 32-39 (January 1993). This switch provides a large scale ATM switch by connecting ATM switches in parallel as illustrated in FIG. 3. The switch provides increased capacity by use of the following structure:
(1) A plurality of multiplexers (MUX) 11 and a plurality of demultiplexers (DMUX) 12 are arranged in parallel on the input side of a plurality of ATM switches 10 are also arranged in parallel;
(2) A plurality of multiplexers (MUX) 13 and a plurality of demultiplexers (DMUX) 14 are arranged in parallel on the output side of the ATM switches 10; and
(3) The ATM switches 10 share traffic load on the cell level or connection level, and exchange cells.
The matrix ATM switch illustrated in FIG. 2 provides advantages in that even when the switch is expanded an internal blocking of traffic does not occur in. However, the disadvantage is that when the switch is expanded K times the capacity of a single ATM switch unit, the number of ATM switch units required is 4K2. For example, when the capacity of the matrix ATM switch is doubled, 16 ATM switch units are required. Thus, a proportionately larger quantity of ATM switch units are required for each unit increase of capacity of the matrix ATM switch.
In the ATM switch illustrated in FIG. 3, if load sharing of traffic is performed at random according to the cell level, there is a possibility of the occurrence of reversing the sequential order of the cells. Thus, to properly reconstruct the cell order a time stamp is necessary on the output side of the switch. Implementation of an ATM switch using a time stamp requires the addition of hardware and complex control thereof. Further, if load sharing of traffic is performed according to the connection level, internally a blocking of traffic in the ATM switch occurs. To remove the blocking of traffic the number of ATM switches installed in parallel is increased or the internal link speed is increased to a level higher than that of the input/output line speed. Thus, similar to the above, the addition of redundant hardware becomes necessary.
Therefore, according to the above, a desired increase in the capacity of a conventional large scale ATM switch is accomplished by increasing the number of ATM switch units. However, the increase in capacity is accomplished by a proportionally larger increase in hardware. In numerous application size is an important consideration, thereby limiting large increases in hardware. However, limiting increases in hardware increases the possibility that blocking of traffic may occur.
An object of the present invention is to provide an ATM switch that can easily be expanded with just minimal hardware additions.
Another object of the present invention is to provide an ATM switch that can be easily expanded by connecting small capacity ATM switch units in parallel to form a large scale ATM switch.
Yet another object of the present invention is to provide a large scale ATM switch having a plurality of ATM switch units connected in parallel, wherein internal blocking of traffic does not occur.
Still yet another object of the present invention is to provide an ATM switch that adds minimal hardware for each unit increase in capacity.
The present invention provides a method of expanding the capacity of an ATM switch suitable for constructing a large scale ATM switch. Specifically, the present invention provides the following for expanding the capacity of an ATM switch. Providing a small capacity ATM switch unit. Connecting others of such ATM switch units in parallel to increase the capacity of the ATM switch to form a large scale ATM switch. The large scale ATM switch expanded in the manner described above does not require an additional new control circuit and a control procedure thereof. The expansion procedure is simple being that it can be accomplished by the addition of minimal hardware. Further, the internal blocking of traffic in the ATM switch does not occur.
In the present invention an increase in the capacity of an ATM switch can be accomplished easily by small additions of hardware. For example, when doubling the capacity of an ATM switch the quantity of a switch is doubled. Thus, when the capacity is increased 4 times, the quantity of the hardware of the switch is increased 4 times. Therefore, in the present invention the expansion of the capacity of an ATM switch is essentially proportional to an increase in the quantity of the hardware added to the ATM switch to accomplish the desired increase.
The present invention also provides control methods for an ATM switch, such as a cell distribution method for an expanded switch, a cell assembling method for each of the switches, and a cell control method for the entire switch. These control methods prevent internal blocking of traffic in the ATM switch even if the capacity of the ATM switch is increased.
The ATM switch of the present invention can easily perform cell distribution and assembling without the need for complex control even when the capacity of the switch is increased. To accomplish this, the present invention provides an ATM switch which exchanges ATM cells received from a plurality of input highways to one of a plurality of output highways based on destination information included in the header of each of the ATM cells. The ATM switch includes a plurality of ATM switch units that exchange the ATM cells, a plurality of cell distributors that distribute the ATM cells received from the input highways to the ATM switch units based on routing information of a header of each of the ATM cells, and a plurality of cell assemblers that assemble the ATM cells exchanged with the ATM switch units and output the ATM cells to one of the output highways based on the destination information of the header of each of the ATM cells. The ATM switch inputs a plurality of cells for the same output line from each of the cell distributors into input lines of each of the ATM switch units in parallel. Each of the ATM switch units performs the same exchange operation independently.
Each of cell distributors includes a buffer memory which accumulates ATM cells received from the input highways, a distributor which distributes the ATM cells read from the buffer memory to an input line of each ATM switch unit, and a control unit which controls the writing and reading of the buffer memory.
Each of the cell assemblers includes a buffer memory that accumulates the ATM cells received from an output line of each of ATM switch units, a demultiplexer that outputs a cell read from the buffer memory to one of the output highways, and a control unit that controls the writing and reading of the buffer memory.
Each cell distributor operates as follows:
(1) A cell received from a plurality of input highways is accumulated in a queue, which is constructed in the buffer memory, corresponding to the output line of ATM switch unit;
(2) A plurality of ATM cells destined for the same output line of an ATM switch unit are read from the queue; and
(3) A plurality of ATM cells destined for the same output line are dispersively input into the same input line of each ATM switch unit in parallel. Each of the ATM switch units perform the same exchange operation independently.
Each cell assembler assembles ATM cells from the output lines of the ATM switch unit each of which as described above performs the same exchange operation. Each ATM cell is output to the output highway which is the destination of the ATM cell.
Each cell distributor of the ATM switch of the present invention includes a dummy cell generator that generates a dummy cell having the same destination information as normal cells which are output to the ATM switch units in parallel. Use of the dummy cell generator permits each of the ATM switch units to perform the same exchange operation independently. Such is possible even if the ATM cells for the same output line from each of the cell distributors are input into the same input line of each of the ATM switch units in parallel and respectively.
When the number of ATM cells, each of which includes the same destination information, output to the ATM switch units in parallel is less than the number of ATM switch units, then the dummy cell generator generates dummy cells each with the same destination information as the ATM cells and sends the dummy cells to ATM switch units. The destination information of the ATM cells, each of which is input into each of ATM switch units, is made the same by this operation. Each cell assembler includes a circuit which detects and discards the dummy cell received from the ATM switch units.